Thermoacoustic refrigeration uses sound waves and helium gas to create cooling power, eliminating the need for complex mechanical components and ozone-depleting gases. It is more environmentally friendly, requires less maintenance, and has higher efficiency potential. Developed at Penn State University, it has been extensively tested and could potentially replace traditional refrigeration methods that have negative environmental impacts.
Thermoacoustic refrigeration, like conventional refrigeration, uses a closed pressure unit. Beyond this commonality, the two methods of refrigeration are very different. Instead of cooling through vapor compression involving complex mechanical components and ozone-depleting gases, thermoacoustic refrigeration uses sound waves instead of a compressor to create cooling power.
A thermo-acoustic unit consists of a regenerator, made up of a pile of fine-mesh window screening material, much like a sieve; two heat exchangers; and a loudspeaker to provide acoustic energy. The loudspeaker is modified to generate highly amplified sound in an environment containing helium, an environmentally friendly inert gas that is converted into cooling energy. The sound wave levels are so high, around 170 decibels, that they can barely be heard by humans; this level is several times higher than an average rock concert. These sound levels can only be achieved in a pressurized, contained gas atmosphere.
Thermoacoustic refrigeration was developed at Penn State University by acoustics experts led by former drummer Dr. Steven Garrett, professor of acoustics and senior scientist. US ice cream moguls Ben Cohen and Jerry Greenfield were researching alternative refrigeration methods that were environmentally friendly. They received financial help from their parent company, Unilever, and joined the Penn State project as a partner.
Thermoacoustic refrigeration is promoted as better than traditional refrigeration on many levels. Not only does it eliminate the need for much of the mechanical components of conventional refrigeration units, it also requires less maintenance and is more environmentally friendly as it uses natural inert gases. Temperature is more easily controlled, which increases the potential for higher efficiency and lower operating costs.
The method was used successfully in the prototype to cool a unit to -11°F (-24°C). This is well below the freezing point of water and more than adequate for successfully storing ice cream. Since Penn State research that began in 2002, many thermoacoustic refrigeration units have been extensively developed and tested. The final working prototype was unveiled at Ben & Jerry’s Waterbury, Vermont facility during Earth Day in 2004.
In the United States and around the world, there are hundreds of millions of residential, industrial, and commercial refrigeration, freezer, and air conditioning units using traditional cooling mechanisms and chemicals. Many traditional refrigerant gases, such as hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs), are believed to have an impact on global warming if disposed of improperly. If the thermoacoustic refrigeration method proves to be a viable and cost-effective alternative, the negative environmental impact of older refrigeration techniques could be minimized and eventually eliminated.
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